1. Field of the Invention
This invention relates to a recording medium, on which to record information.
2. Description of the Prior Art
While microfilms have so far been used as the medium for high density recording of information, various other versions of recording medium such as high density magnetic recording medium, optical memory medium, and so forth have been brought to attention of all concerned as the medium for electronic files. For instance, amorphous alloy films composed of rare earth metals and transition metals has been known to be useful as the magneto-optical recording medium. Of these materials, GdTbFe has a large Kerr rotational angle and a Curie point of 150.degree. C. or so, hence it provides a recording medium excellent in its write-in and read-out efficiency. GdTbFe, however, is inferior in its corrosion-resistance as is the case with other amorphous magnetic materials, which causes not only deterioration in the magnetic characteristics in a highly humid atmosphere, but also increase in number of pin hole in apperance. As the measures for preventing such corrosion or increase in the pin holes from taking place, there have been adopted various methods such as, for example, providing a protective layer on the magnetic layer, sticking the layers with a moisture-resistance adhesive layer, and so forth. These preventive measures are also not able to attain perfect elimination of the abovementioned corrosion or increase in the pin holes, nor produce any effect against the pin holes to be generated in the course of forming the magnetic layer.
As such, occurrence of the defects in the recording layer at its formation or after its formation is not limited to the abovementioned magneto-optical recording medium, but also they tend to occur in those heat-mode recording mediums of bismuth-, rhodium-, tellurium-, or organic-compound-series, wherein information is recorded in the form of pits, or in those recording mediums which change their form upon heat application. In such defective portion in the recording medium, no information can be recorded, which is represented as the so-called "error-rate".
FIG. 1 of the accompanying drawing illustrates one embodiment of the conventional magneto-optical recording medium. In the drawing, a reference numeral 1a designates a glass or plastic substrate, on which a reflection preventive layer 2a, a magnetic layer 3a, and a protective layer 4 are sequentially formed by the vacuum deposition or sputtering or other methods, and then another substrate 1b of glass of plastic is sticked onto the protective layer 4 through an adhesive layer 5. In this laminar structure, the reflection preventive film 2a is of ZrO.sub.2 having a refractive index of 2.0, the magnetic layer 3a is of GdTbFeCo having a complex refractive index of 2.53-i3.31 for a wavelength of 800 nm, and the protective layer 4 is of SiO having the refractive index of 1.7.
FIG. 2 shows a spectral reflectance in case the substrate at the reading side of the recording medium is of sheet glass, it being understood that the surface reflection of the glass plate is not included. An optical film thickness of the reflection preventive layer 2a is approximately 160 nm, which corresponds to a quarter of the wavelength of 800 nm in taking a phase shift to occur at the interface between the reflection preventive layer 2a and the magnetic layer 3a into consideration. The magnetic layer 3a has a thickness of about 100 nm, which does not permit light to pass through it. In the conventional structure as shown in FIG. 1, where the magnetic layer 3a contains pin holes, there are no write-in and read-out operations to be done possibly as a matter of course.